Streptococcus pneumoniae (SP) is the leading bacterial pathogen causing pneumonia, meningitis and sepsis in children. About 1 million children die because of SP infections every year worldwide (O'Brien, K. L., et al., Lancet 374: 893-902, 2009).
Current licensed pneumococcal vaccines are exclusively targeted at the capsular polysaccharide (CPS) of SP, and these vaccines provide strictly serotype-specific protection. Although the poor immunogenicity of CPS antigens has been overcome by a pneumococcal CPS-protein conjugate vaccine (PCV), protection is still serotype-specific and the high cost of PCV reduces the vaccination coverage. Moreover, studies of nasopharyngeal colonization by SP have shown that the vacated niche was promptly occupied by non-vaccine pneumococcal serotypes that are potentially capable of causing disease. Thus, in the long term, the widespread introduction of CPS and PCV might merely alter the serotype distribution of invasive pneumococcal disease, without reducing the overall SP disease burden (for review, see Kadioglu, A. et. al., Nature Reviews Microbiology 6: 288-301, 2008).
The most promising approach to date has been development of vaccines that are based on pneumococcal antigens that contribute to virulence and are common to all serotypes. Native protein antigens such as PsaA, or immunogenic fragments thereof, can stimulate an immune response when administered to a host, but such antigens are poorly immunogenic and are poor mucosal immunogens. As SP must first gain entry to a host through mucosal surfaces in order to establish an infection, it is desirable to induce mucosal immunity (e.g., mucosal secretory IgA antibodies) in addition to an antigen-specific IgG response. Indeed it has been demonstrated that without induction of Th1 responses, CD4+ T-cell-deficient mice were unable to clear nasopharyngeal colonization.
There is a need for a broad-spectrum pneumococcal vaccine that induces mucosal immunity.
In general, modified proteins, such as lipidated proteins, are more immunogenic than unmodified proteins. Proteins in certain vaccine products have been prepared by expression in E. coli using recombinant technology, however, E. coli is generally viewed as not suitable for producing modified proteins, particularly lipidated proteins, as E. coli cells lipidate naturally lipidated proteins poorly and do not produce non-naturally lipidated proteins in lipidated form.
U.S. Pat. No. 7,833,776 discloses production in E. coli of a lipidated fusion protein containing a lipidating sequence derived from Ag473 and a target polypeptide. There is disclosed a lipidating sequence containing at least the N-terminal 40 residues (D1) of Ag473 to facilitate lipidatation in E. coli of a fusion protein. Methods of producing a fusion protein in lipidated form are also described.
U.S. Pat. No. 7,960,535 describes recombinant lipidated PsaA proteins and recombinant constructs from which such lipidated PsaA proteins may be expressed. There are described lipidated PsaA proteins in which lipidation is effected by the use of a heterologous leader sequence derived from the ospA gene of Borrelia burgdorferi, which leader sequence is joined in translational reading frame with the psaA structural gene. The invention also provides methods of preparation of lipidated PsaA proteins and use of such proteins in immunological compositions. Also provided are vaccines comprising immunogenic lipidated PsaA proteins and methods of use of such vaccines in the prevention and treatment of S. pneumoniae infection.
U.S. Pat. No. 6,538,118 describes heterologous lipidated proteins formed recombinantly in an expression system such as E. coll. The heterologous lipidated protein has a leader sequence which does not naturally occur with the protein portion of the lipidated protein. The lipidated protein can have the Borrelia OspA leader sequence. The protein portion can be OspC, PspA, UreA, Ure B, or a fragment thereof. Methods and compositions for forming and employing the proteins are also disclosed and claimed.
U.S. Pat. No. 8,771,990 describes methods of producing a recombinant lipidated polypeptide in E. coli. The method includes providing an E. coli host cell adapted to express a recombinant lipidated polypeptide; and culturing the E. coli host cell in a minimal medium under conditions that allow expression of the polypeptide in lipidated form.